Abstract

The aviation industry is exploring the economic viability and environmental sustainability of the use of alternative fuels to power aircraft main engines and auxiliary power units. The International Civil Aviation Organization is also developing a regulatory standard for aircraft engine nonvolatile particulate matter (nvPM) emissions to meet the growing public demand for improvement in air quality. This study compared the nvPM emissions in the exhaust stream of a small (<26.7 kN thrust) mixed turbofan aircraft engine burning a conventional Jet A fuel as well as a Sasol isoparaffinic kerosene (IPK) fuel derived from coal, using a standardized sampling and measurement system. The goal of the study was to demonstrate the regulatory system on a small mixed turbofan engine and to assess the suitability and limitations of using such systems for turbofan engines burning fuels with different fuel properties. Significant reductions in both nvPM number- and mass-based emission indices were observed with the IPK fuel across the full spectrum of engine thrust settings. The percent reduction in nvPM mass-based emissions was higher than the reduction in nvPM number-based emissions for the corresponding engine thrust settings because smaller and fewer particles were generated with IPK fuel combustion. PM size distribution mean diameters for the IPK fuel were found to be smaller than that for Jet A. The composition of the organic PM emissions for the two fuels was almost identical, and the organic PM was also found to be proportional to the soot concentration. The nvPM mass-based emissions for the mixed turbofan engine measured with the standardized system exhibited a high degree of measurement uncertainty at low engine thrust settings. This limitation was not encountered for nvPM number-based emissions.